Threading of Conformationally Stable Calix[6]arene Wheels Substituted at the Methylene Bridges

Calix­[6]­arenes
disubstituted at the methylene bridges, which are
stable in the cone or 1,2,3-alternate conformation, form pseudorotaxanes
with dialkylammonium axles. The cone wheel-based pseudorotaxanes are
10–100 times more stable than those obtained with the native
conformationally mobile calix[6]­arene wheel, as a consequence of their
higher degree of preorganization. The threading of conformationally
stable 1,2,3-alternate calix[6]­arenes is unprecedented in the literature.
Therefore, very peculiar NMR features are here evidenced for this
threading process involving the less symmetrical 1,2,3-alternate calix[6]­arene
conformation, which implies a peculiar rototranslation motion of the
axle.